Dielectric and anelastic spectroscopy: a powerful combined tool for characterizing multifunctional ceramics

Dielectric and anelastic spectroscopies are complementary techniques and their combination allows valuable information to be obtained in the field of multifunctional materials. Whereas the dielectric spectroscopy measures the dielectric susceptibility ?(?,T) and it is sensitive to fluctuations of electric dipoles, the anelastic spectroscopy measures the elastic compliance or elastic susceptibility s(?,T) and it is sensitive to fluctuations of elastic dipoles. Both susceptibilities are complex, their immaginary part being due to the delayed response of the mobile defects coupled to the electric field/stress. The great advantage of using a combination of both techniques is that the anelastic measurements are insensitive to free charges, therefore it is possible to measure the dynamics of ions also in the presence of free charges. Two main types of investigations have been pursued by the combination of these techniques: the study of structural phase transitions and the study of microscopic mechanisms associated with the presence of defects, both important for the knowledge and development of multifunctional materials. We have applied this approach for different functional materials with perovskite framework: multiferroic, ferroelectric and relaxor ferroelectric ceramics, and organic-inorganic perovskite photovoltaics. Thanks to the combination of the two spectroscopies, it has been possible to probe more accurately the structural transitions involving the antiferrodisortive tilt modes of the octahedra in PZT [1] and NBT-BT [2]. It was also possible to evidence incipient phase separation in lead titanate-based multiferroics [3]. Moreover, since the elastic response is insensitive to free charges, it has been used to probe the piezoelectric response even in unpoled ceramics [4] and for the study of coexisting ferroelectric and metallic states [5]. The combination of the two techniques allowed also new features to be revealed on the reorientation dynamics of the organic molecules in MAPbI3 photovoltaic organic-inorganic perovskites and the hindrance of their ferroelectric order by coupling with the tilt modes [6]. 1. F. Cordero, F. Trequattrini, F. Craciun, C. Galassi, Phys. Rev. B, 87 (2013) 094108 2. F. Cordero, F. Craciun, F. Trequattrini, et al., Phys. Rev. B, 81 (2010) 144124 3. F. Craciun, F. Cordero, B. Vasile, et al., Phys. Chem. Chem. Phys., 20 (2018) 14652 4. F. Cordero, F. Craciun, F. Trequattrini, C. Galassi, Phys. Rev. B, 93 (2016) 174111 5. F. Cordero, F. Trequattrini, F. Craciun, et al., Phys. Rev. B, 99 (2019) 064106 6. F. Cordero, F. Craciun, F. Trequattrini, et al., J. Phys. Chem. Lett., 9 (2018) 4401